The efficiency rating on a PSU is simply a rating for how well the PSU converts the AC power it recieves from the outlet to DC power the components of the PC can use.

So, for simplicy sake, lets say your PC components are drawing 100w of power. If you have a PSU that is 80% efficient, it will really draw 125w from the AC outlet.

I've seen people say that you take the Wattage rating of the PSU, and the efficiency is how much power the PSU can really output for your component. That means that a 500w PSU, rated for 80% efficiency will only be able to supply 400w. This is wrong. A 500w PSU should be able to output 500w to your PC components in one form or another. Efficiency has nothing to do with this.

Well if I have a PSU that is rated for 80% efficiency, where does the other 20% go?

Simple answer: Heat. Any electricity not converted from AC to DC is given off as heat.

Will there ever be 100% efficient Power Supplies?

I'm one that lives by the moto "nothing is impossible", so I'm not going to say flat out no. However, I will say that it is highly highly unlikely, and none of use will probably see it in our lifetimes or our childrens lifetimes.

If I have a 500w PSU, does that mean it will always draw 500w of power?

No. The amount of power drawn is determined by the components of the computer and how much they require. The amount of power drawn will only be equal to what is needed, and no more. If all the components of a computer require 300w to run, then the "load" on the PSU will be 300w and hence the power draw of the PC will always be 300w+Inefficiency no matter if it is a 500w PSU or a 1000w.

So what do the different 80 Plus ratings mean?

The basic 80 Plus rating means that the PSU is rated for at least 80% efficiency at 20% load, 50% load, and 100% load.

The 80 Plus Bronze rating means that the PSU is rated for at least 82% efficiency at 20% load, 85% at 50% load, and 82% at 100% load.

The 80 Plus Silver rating means that the PSU is rated for at least 85% efficiency at 20% load, 88% at 50% load, and 85% at 100% load.

The 80 Plus Gold rating meas that the PSU is rated for at least 87% efficiency at 20% load, 90% at 50% load, and 87% at 100% load.

The 80 Plus Platinum(bet you didn't know there was a Platinum) rating means that the PSU is rated for at least 90% efficiency at 20% load, 92% at 50% load, and 89% at 100% load.

Now, that doesn't mean that the PSUs perform exactly at those numbers, but they are close enough, and of course you probably aren't going to use exactly 50% load or whatever, but it is close enough to give a good idea of what a PSU is capable of.

What is in it for me?

Ah, good question! I made some quick charts to show how much you save in a year over a standard 80% efficient 80 Plus PSU by going with an 80 Plus Bronze/Silver/Gold/Platinum:

Some information about these charts.

This assumes a 12 Cent/KwH energy rate, if you pay more for your electricity, then the numbers will be slightly higher.

This also assumes the computer is running an average of 10 hours per day, again if your computer is on longer, then your savings will be greater.

Also remember, "load" in that chart is the percentage load of the capability of the PSU. So 20% load on the 500w PSU would be 100w, that is actually a pretty good area for where a computer would idle.

Now of course the other benefit, as I kind of hinted at earlier, is heat. The PSU will put out less heat. Now how much less heat will a Gold PSU output over a Bronze? Well probably not a whole lot, certainly not enough to worry about since it is being expelled right out the back anyway. However, I made a few more charts to show exactly how much less heat will be output by the different rated power supplies compared to an 80 Plus PSU.

So with an 800w PSU, even at full load, you are looking at about 100w of heat. That might seem like a lot, but to put it in perspective, space heaters generally start at 500w and go up from there. A 500w space heater will warm a 10' x 10' room up about 10°F, so the extra 100w from the inefficiency might make the room temp rise 2°F.

Of course that heat also builds up in the PSU, as a hot PSU looses efficiency. However, that comes down to the cooling system in the PSU, and how effective it is.

What if I'm upgrading from a non-80 Plus Power Supply, what are my savings?

Ah, another good question, and another few charts.

This first chart is how much money you will save over a year. Again, the same rules as above apply, 12 Cents per Kwh, 10 hours per day running.

This chart also assumes that your current PSU is 70% efficient at 20% and 100% load, and 75% efficient at 50% load. Without measuring the exact amount, it is impossible to know what efficienty your current PSU is really running at, but these number are pretty good guesses for a non-80 Plus PSU.

Now what about the heat savings? Well, here is another chart.

Conclusion:

Is a 80 Plus Gold PSU necessary? Well, I'm not going to answer that for you, that is up to you to decide. Look at the savings over a year, and make the decision. How many years are you going to be using this PSU? Will it make up for the price difference? You have to answer all this before deciding if a 80 Plus gold PSU is right for you, or if a cheaper 80 Plus Bronze is the way to go.

I can say, personally, I'd be fine with an 80 Plus Bronze Power Supply and the only way I'd go with an 80 Plus Gold would be if the prices was very close. Of course an 80 Plus Gold PSU would probably be a great savings for anyone building dedicated Folding or Crunching machines.

very nice read. i too have heard many people think the efficiency is what it can actually output and i always have to tell them they're wrong lol. Nice for new people to read as well, should be stickied.

The transformers aren't 100% efficient is because there is energy loss, some of it is lost to heat ect. That's why there probably wont be 100% efficient because some it is always lost; unless they invent some new transformer or something else to do the job of a transformer.

Power grid transformers are 98% and above efficient, Experimental transformers using superconducting windings achieve efficiencies of 99.85% even such a small increase saves a lot of money.

EDIT: Efficiency is just that the computer needs like 250w for example but it will draw more than that because they lose energy.

A pc needing 250w will use about 294w at 85% efficiency.
It needs the extra because if it just drew just 250w from a wall it wouldn't be able to supply 250w when its converted by the transformer. It loses about 46w at 85% efficiency. So it needs to draw more power to make up the lost energy.

I think I'm going to add a few different usage senerios to make up a few different charts to add to the one I've got.

What power supply ratings does everyone thing I should use?

I was thinking adding a chart for 1000w, 650w, 500w?

Also adding a chart for 12 and 24 hours usage per day?

Oh well, I'll do that tomorrow, I posted that just before leaving work, and I just made it home...I love commuting...

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take your time, and make segments. cover all the basics of PSU's - for example, i still run into people who think a 500W PSU draws 500W all the time. I'd suggest clarifying a little bit more about upgrading PSU's as well, you dont mention older PSU's for comparison - a cheap passive PFC model vs an 80+ gold, would save a toooon of power, for example.

could you just set up graph so that it simply goes every 100 watts or so? i think it'd just look nicer with more info and be easier to grasp.

like i'm thinking 500-1000 with 100watt intervals on bottom of graph. N then you'd have like 4 different colored lines for the different 80% ratings. With the left side covering the extra wattage you draw from an outlet.

Like if i got it correctly. 500watts at 80% efficiency will actually draw ~600watts due to the efficiency at converting dc to ac? That's my understanding and im just now starting to get into PSU's lol

could you just set up graph so that it simply goes every 100 watts or so? i think it'd just look nicer with more info and be easier to grasp.

like i'm thinking 500-1000 with 100watt intervals on bottom of graph. N then you'd have like 4 different colored lines for the different 80% ratings. With the left side covering the extra wattage you draw from an outlet.

Like if i got it correctly. 500watts at 80% efficiency will actually draw ~600watts due to the efficiency at converting dc to ac? That's my understanding and im just now starting to get into PSU's lol

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you're on the right track.

in order for an 80% efficient PSU (lets assume its actually 80% efficient, for this) to deliver 500W of power to your system (which is a very high figure, unless you're running 2 or more video cards) would draw 600W at the wall.

that 100W extra would end up being heat output inside the PSU - so in that example, going from an 80% PSU to a 90% one, would save you 50W of power - as well as 50W of heat.

also keep in mind the easy comparison to an electric heater. i've got a small one here that goes from 1000W to 2000W - you could say that saving 100W of heat output from your PC, is saving you 1/10th the heat the heater would have made (or alternately, for every ten hours your PC is on, its the same as having that heater on for one hour)

when you think of how hot a room can get from having a heater (even on low) for an hour, you start to realise just how much these heat and power savings can really add up.

mussels weren't big enough XD. yea i noticed there's only a handful of people that do em.

OT: sorta lol, have we created a thread section that's just strait up full of informative threads like this? if not we should, just like a thread section not postable unless a thread is moved by a mod for its informative status.